1. Cross Reference To Related Application
The applicant of this invention has filed the application (Ser. No. 775,028 on Sept. 11, 1985) regarding the digital convergence to the U.S. Patent Office prior to this invention. This invention relates to an improvement of this application.
2. Field Of The Invention And Related Art Statement
The present invention relates to a digital convergence apparatus for digitally performing the convergence correction of color television sets (including video monitors and projector-type color television sets).
The convergence correction of color television sets has conventionally been performed by an analog process, using a correction signal derived from the horizontal and vertical deflection signals.
When the screen is large, and with a great and variable distance between the screen and the projector of a projector-type color television set, and when the screen surface is rough, such as in a projector-type color television set of the three-tube type, the allowable range of misconvergence or misregistration is narrow. Thus, a convergence correcting apparatus having a high degree of accurancy has been needed. Therefore, the conventional projector-type color television set, in which the convergence is adjusted by an analog process, is equipped with a plurality of variable controls in order to finely adjust the convergence.
The shape of the projection screen used, for example, with a projector-type color television set of the triple-tube type, affects the required amount of convergence correction according to the receiving standards. The raster shape, which is the ratio of the vertical length to the lateral length (hereinafter, referred to as an aspect ratio) derived by reproducing a video signal of the NTSC system is (3:4). Another aspect ratio is derived by reproducing a video signal of a high quality television set, viz. (3:5). There is still another raster shape in which the aspect ratio is (1:2) corresponding to the cinema scope aspect ratio, and the like. When the screen size or aspect ratio change, the characteristic of the convergence also changes. Therefore, when the size of screen which is projected and/or aspect ratio change, it is necessary to readjust the convergence.
In the case of executing the convergence correction by the analog process, in order to cope with the aspect ratios of various kinds of standards, it has been proposed to use a separate set of manual controls for each different size or shape of screen to be used. For instance, a first control is used when the aspect ratio is (3:4), a second control when the aspect ratio is (3:5), a third control when the aspect ratio is (1:2), and the like. These separate controls are switched as needed, thereby controlling the convergence.
However, in the projector-type color television set, a plurality of controls for the convergence correction are needed with respect to the screen size for each different standard. Thus, if individual controls are used, the number of controls increases by a number which is a multiple of the number of standards to be accomodated. Therefore, a very large number of (e.g., at least thirty to fifty) manual controls are necessary, so that the adjustment becomes fairly complex and difficult, and the circuit scale also increases.